High voltage d-c current limiter

DETAILED DESCRIPTION This invention is predicated upon a new and unique sub-circuit system or current limiter that utilizes a plurality of PTC resistors connected in series such that the assembly system will have an overall voltage capacity equal to the sum of voltage capacity limits of the PTC resistors, and which is not time limited in any way whatsoever.
Furthermore, there is no need that the PTC resistors be identical or even similar in nature, form or chemistry, or that they all be subjected to the same thermal environments.
The current limiter of this invention can utilize as many PTC resistors in series as necessary to achieve whatever blocking voltage capacity is desired, and can be incorporated within virtually any system or circuit to function as a self-resetting fuse or circuit breaker without any concern for time limitations.
Accordingly, the current limiter of this invention can be utilized as are conventional, independent PTC resistors to protect virtually any desired circuit from overload condition, which includes the self-resetting feature, and which can be adapted for use at virtually any desired voltage level.
In particular, the current limiter of this invention has found particular utility in combination with 74 volt, d-c, railroad locomotive power systems and circuits, which are utilized to operate most of the locomotive control systems, such as the electronic air brake and throttle control, as well as other locomotive systems and circuits.
In essence, the current limiter, or sub-circuit system of this invention involves the use of a plurality of PTC resistors connected in series, wherein each PTC resistor is individually connected in parallel with a zener diode, with each zener diode having a zener voltage less that the predetermined voltage capacity limit; i.
e.
, break-down voltage, of the PTC resistor connected in parallel therewith.
The current limiter system will have an overall voltage capacity limit substantially equal to the sum of the voltage capacity limits of all the zener diodes in the assembly system, which may approach the sum of the voltage limits of all the PTC resistors in the series